1. Field of the Invention
The present invention relates generally to a switching circuit using an MOS field effect transistor, and is directed more particularly to a switching circuit using a MOS field effect transistor in which the discharging current of an inductive load is prevented from being flowed between the substrate and drain electrode of the transistor.
2. Description of the Prior Art
In the art, such a switching circuit has been proposed as the output stage of a pulse width modulating amplifier in which a pair of complementary MOS field effect transistors (which will be hereinafter referred to as MOS-FETs) are connected in push-pull relation. In this case, since the MOS-FET is superior in switching characteristic, the frequency of a carrier for the pulse width modulating amplifier can be selected high, but on the contrary, the discharging current from an inductive load flows through the P-N diode connection between the substrate and drain electrode of the MOS-FET. In this case, since the switching speed of the diode is low, the inherent switching characteristic of the MOS-FET can not be utilized sufficiently.
Up to now, there has been proposed no such a switching circuit which uses a MOS-FET free from the above prior art defect and is effective as the output stage of a pulse width modulating (PWM) amplifier.